Is it obligatory to apologize to one's mother for not responding to her when she calls, fearing her past reactions? And what should I do if I stopped drinking coffee to please her, then desired it again? And is showing no expression on one's face as a reaction to the mother's scolding and her nervous demeanor considered correct behavior?

If drinking coffee does not cause harm, there is no objection to drinking it despite the mother's prohibition, while being careful to conceal it from her to avoid vexing her. If the mother speaks words that are displeasing, there is no objection to remaining silent while keeping one's face expressionless. When the mother calls, one must respond and fulfill her request courteously, and apologizing to her when she is angry is not a blow to dignity but rather enhances it. One must strive to be dutiful and benevolent to the mother, and be wary of obsessive thoughts regarding parental piety and other matters.